In multilayered polyamide-based tubes for food packaging, polyolefin-based resins are generally used as the layer that is in contact with the packaged food, such as processed meat. There is a method in which a corona treatment or the like is applied to the surface of the layer that is in contact with the packaged food to improve the adherence to the packaged food (for example, Patent Documents 1 to 3).
Such a technique makes it possible to obtain a multilayered polyamide-based tube for food packaging that is free from blocking between the inner surfaces thereof immediately after film production, and free from opening problems. However, depending on the conditions under which the multilayered polyamide-based tube for food packaging is stored before being used, blocking between the inner surfaces thereof may occur to remarkably decrease the opening properties. In particular, if a packaging material with a high low-temperature shrinkage ratio is wound around a paper tube immediately after being produced, the winding tightens as time passes. This causes blocking between the inner surfaces of the multilayered tube due to the stress that is generated.
Patent Document 1: Japanese Unexamined Patent Publication No. 1989-64845
Patent Document 2: Japanese Unexamined Patent Publication No. 1990-135230
Patent Document 3: Japanese Unexamined Patent Publication No. 1999-155473